JohnSSM Posted January 22, 2015 Share Posted January 22, 2015 My understanding of red shift is that objects moving away from an observer take on a red shade because the photon's frequency is reduced and wavelength is increased (stretched) as it travels from the moving object towards our eye (the distance between the two grows as the photon travels at us)...And being in front, one would see a blue shift as the photon's frequency is increased (compression)...cuz the distance between the 2 objects is getting smaller as it approaches us...so expanding space would be seen with a red shift, and compressing space is seen as blueWe also see redshift in objects with massive gravity as well...in comparison to the above, gravity would also then represent an increase in the wavelength of light. And imply that objects with more gravity are moving away from us in this relative comparison of the effects of motion on space-time and the effects of gravity on space-time.And it doesnt make much sense to me to think of gravity as a "separation" of objects...that would imply an acceleration away from two objects...but gravity seems to imply an acceleration of objects towards each other...How does one get RED when the force of gravity would seem to imply a shrinking of space between 2 objects...and we know we see red when 2 objects are increasing the space between them? not shrinking it...I know we do get red, but doesnt this imply that 2 objects within a common gravitational field would be seen as falling away, not together? Falling together seems to create a blue shift...SO im stumped... Link to comment Share on other sites More sharing options...
Aminoxyl Posted January 22, 2015 Share Posted January 22, 2015 (edited) I am no expert here, but as the gravitational force of the object (in this case a photon) nears another object let's say a large planet then the photons should be travelling faster towards the planet the closer they are. In this case as an independent observer you should observe the wavelength being stretched, as although we have the planet and photon becoming increasingly closer to one another it is stretching the wavelength because it is "pulling" it in. O | | | | | | | | | | | | ||||||||| If you take the O as a planet and | as points in our wave. Could you see how if this planet was facing directly in front of you it would cause a red shift? Relative to that planet (I am assuming) it would cause a blue shift, but observing another planet you would see a red shift as the photons are slowed down before they exit the planets gravitational pull etc. Here's a nice little article for you C: http://einstein.stanford.edu/content/relativity/q56.html Edited January 22, 2015 by Aminoxyl Link to comment Share on other sites More sharing options...
xyzt Posted January 22, 2015 Share Posted January 22, 2015 My understanding of red shift is that objects moving away from an observer take on a red shade because the photon's frequency is reduced and wavelength is increased (stretched) as it travels from the moving object towards our eye (the distance between the two grows as the photon travels at us)...And being in front, one would see a blue shift as the photon's frequency is increased (compression)...cuz the distance between the 2 objects is getting smaller as it approaches us...so expanding space would be seen with a red shift, and compressing space is seen as blue We also see redshift in objects with massive gravity as well...in comparison to the above, gravity would also then represent an increase in the wavelength of light. And imply that objects with more gravity are moving away from us in this relative comparison of the effects of motion on space-time and the effects of gravity on space-time. And it doesnt make much sense to me to think of gravity as a "separation" of objects...that would imply an acceleration away from two objects...but gravity seems to imply an acceleration of objects towards each other... How does one get RED when the force of gravity would seem to imply a shrinking of space between 2 objects...and we know we see red when 2 objects are increasing the space between them? not shrinking it... I know we do get red, but doesnt this imply that 2 objects within a common gravitational field would be seen as falling away, not together? Falling together seems to create a blue shift... SO im stumped... You are mixing gravitational redshift with cosmological redshift. The former is created by the difference in gravitational potential, the latter is created by the increased separation between emitter and receiver (it is similar but not identical to Doppler redshift). Link to comment Share on other sites More sharing options...
Mordred Posted January 22, 2015 Share Posted January 22, 2015 (edited) There is Three main forms of redshift, Cosmological redshift is due to space expansion Gravitational redshift is due to photons climbing into and out of gravity wells Doppler redshift is due to motion This article covers the three of them http://cosmology101.wikidot.com/redshift-and-expansion Keep in mind there are variations on the formulas for reasons such as transverse redshift etc. (Transverse different angles ie object moving left to right at different angles) Edited January 22, 2015 by Mordred Link to comment Share on other sites More sharing options...
xyzt Posted January 22, 2015 Share Posted January 22, 2015 (edited) Keep in mind there are variations on the formulas for reasons such as transverse redshift etc. (Transverse different angles ie object moving left to right at different angles) "Transverse redshift" is simply a forme of Transverse Doppler Effect which, BTW can be EITHER redshift or(!) blueshift. There is an angle, called critical angle, for which there is zero shift, at the boundary between red and blueshift. Edited January 22, 2015 by xyzt Link to comment Share on other sites More sharing options...
imatfaal Posted January 22, 2015 Share Posted January 22, 2015 "Transverse redshift" is simply a forme of Transverse Doppler Effect which, BTW can be EITHER redshift or(!) blueshift. There is an angle, called critical angle, for which there is zero shift, at the boundary between red and blueshift. Yeah - understanding the transverse doppler effect is a real work-out that tests your understanding of relativity; at the point of closest point of approach of two objects light received will be blue-shifted but light emitted will be red-shifted. This was a major new testable prediction of special relativity http://en.wikipedia.org/wiki/Relativistic_Doppler_effect#Transverse_Doppler_effect Link to comment Share on other sites More sharing options...
Mordred Posted January 22, 2015 Share Posted January 22, 2015 "Transverse redshift" is simply a forme of Transverse Doppler Effect which, BTW can be EITHER redshift or(!) blueshift. There is an angle, called critical angle, for which there is zero shift, at the boundary between red and blueshift. I agree it was one example of a variation I should of specified that example applies to Doppler. I didn't want to get into corrections to the cosmological redshift as that gets too distracting to the OPs question. Link to comment Share on other sites More sharing options...
JohnSSM Posted January 22, 2015 Author Share Posted January 22, 2015 There are 2 graphics on this page that are troubling me...http://en.wikipedia.org/wiki/Relativistic_Doppler_effect#Transverse_Doppler_effectIn diagram 1 (top of page) we see red shift as I understand it...the light goes red as the grid spreads out behind an object with motion...IN diagram 2 (right below it) we see the grid compressing behind an object with motion, but still it shifts red...Is diagram 2 mistakenly backwards with its grid effects or is THIS the transverse effect? In either case, it seems the same example of motion to the right, with reversed grid effects... Link to comment Share on other sites More sharing options...
Janus Posted January 22, 2015 Share Posted January 22, 2015 There are 2 graphics on this page that are troubling me... http://en.wikipedia.org/wiki/Relativistic_Doppler_effect#Transverse_Doppler_effect In diagram 1 (top of page) we see red shift as I understand it...the light goes red as the grid spreads out behind an object with motion... IN diagram 2 (right below it) we see the grid compressing behind an object with motion, but still it shifts red... Is diagram 2 mistakenly backwards with its grid effects or is THIS the transverse effect? In either case, it seems the same example of motion to the right, with reversed grid effects... Diagram 2 combines both Doppler shift and aberration. Aberration is the apparent change in the direction light is coming from due to the difference in the relative velocity of source and observer. It is a akin to the effect that when you are driving in rain that is falling straight down, it appears as if the rain is coming at you at an angle. Link to comment Share on other sites More sharing options...
Mordred Posted January 22, 2015 Share Posted January 22, 2015 (edited) That second image is specifically showing aberration of light see the link provided under the image. http://en.m.wikipedia.org/wiki/Aberration_of_light I see Janus best me to it Edited January 22, 2015 by Mordred Link to comment Share on other sites More sharing options...
xyzt Posted January 22, 2015 Share Posted January 22, 2015 Yeah - understanding the transverse doppler effect is a real work-out that tests your understanding of relativity; at the point of closest point of approach of two objects light received will be blue-shifted but light emitted will be red-shifted. This was a major new testable prediction of special relativity http://en.wikipedia.org/wiki/Relativistic_Doppler_effect#Transverse_Doppler_effect Correct, it is the foundation of the Ives-Stilwell experiment, one of the most stringent tests of SR. Einstein conceived it and Herbert Ives, despite of being a convinced anti-relativist, executed it. 2 Link to comment Share on other sites More sharing options...
JohnSSM Posted January 22, 2015 Author Share Posted January 22, 2015 (edited) That second image is specifically showing aberration of light see the link provided under the image. http://en.m.wikipedia.org/wiki/Aberration_of_light I see Janus best me to it Aha...aberration is a different effect with the observer in the moving object...in my own examples, the observer was looking at light FROM the moving object...aberration seems to effect the light which the observer on the moving object sees... Good call...that solves that... I dont have an answer to my original question yet, but I am reading... There is Three main forms of redshift, Cosmological redshift is due to space expansion Gravitational redshift is due to photons climbing into and out of gravity wells Doppler redshift is due to motion These red shift examples all seem to follow the same rules though...space expansion is akin to "motion away from" and both of those should be akin to whatever creates the same effect in gravity's case.... If gravitational redshift is created by photons "climbing" into and out of gravity wells, arent we just saying that gravity wells have the same spacetime characteristics as the space-time behind a quickly a moving object? That effect is akin to spacetime being stretched (the spacetime behind a moving object)...and they both create redshifts... Alas...I am still reading... IS it accurate to say that abberation causes the tranverse effect of shifting? Edited January 22, 2015 by JohnSSM Link to comment Share on other sites More sharing options...
imatfaal Posted January 22, 2015 Share Posted January 22, 2015 Correct, it is the foundation of the Ives-Stilwell experiment, one of the most stringent tests of SR. Einstein conceived it and Herbert Ives, despite of being a convinced anti-relativist, executed it. Thanks - I never knew the story of Ives. Shows the magnificence of our scientific method - and a great deal of personal intellectual integrity - that such an experiment by a firm believer in an alternative explanation can still be used to bolster Einstein's explanation. Lovely and quite sad quote from his friend H P Robertson "Ives' work in the basic optical field presents a rather curious anomaly, for although he considered that it disproved the special theory of relativity, the fact is that his experimental work offers one of the most valuable supports for this theory, and his numerous theoretical investigations are quite consistent with it ... his deductions were in fact valid, but his conclusions were only superficially in contradiction with the relativity theory—their intricacy and formidable appearance were due entirely to Ives' insistence on maintaining an aether framework and mode of expression. I ... was never able to convince him that since what he had was in fact indistinguishable in its predictions from the relativity theory within the domain of physics, it was in fact the same theory... http://en.wikipedia.org/wiki/Herbert_E._Ives 1 Link to comment Share on other sites More sharing options...
xyzt Posted January 22, 2015 Share Posted January 22, 2015 (edited) Thanks - I never knew the story of Ives. Shows the magnificence of our scientific method - and a great deal of personal intellectual integrity - that such an experiment by a firm believer in an alternative explanation can still be used to bolster Einstein's explanation. Lovely and quite sad quote from his friend H P Robertson http://en.wikipedia.org/wiki/Herbert_E._Ives Yes, it is a fantastic story of integrity. As an aside, we owe to H.P.Roberson the first test theory of SR. One can say that Robertson was for (the) theory (of SR) what Ives was for the experimental test. It was Ives insistence on testing SR that inspired Robertson to create the theoretical framework for the test theories of SR. To date, the Ives-Stilwell experiment is a pillar (together with MMX and KTX) of the test theories of SR. It was Robertson as well who proved that the three tests are the necessary and sufficient set. Edited January 23, 2015 by xyzt Link to comment Share on other sites More sharing options...
JohnSSM Posted January 23, 2015 Author Share Posted January 23, 2015 Yes, it is a fantastic story of integrity. As an aside, we owe to H.P.Roberson the first test theory of SR. One can say that Robertson was for (the) theory (of SR) what Ives was for the experimental test. It was Ives insistence on testing SR that inspired Robertson to create the theoretical framework for the test theories of SR. To date, the Ives-Stilwell experiment is a pillar (together with MMX and KTX) of the test theories of SR. It was Robertson as well who proved that the three tests are the necessary and sufficient set. I read over it as well...Ives musta been an interesting fella... Link to comment Share on other sites More sharing options...
Mordred Posted January 23, 2015 Share Posted January 23, 2015 Thanks for sharing that zyxt, I'll have to study that bit of history in more detail. Link to comment Share on other sites More sharing options...
xyzt Posted January 23, 2015 Share Posted January 23, 2015 Thanks for sharing that zyxt, I'll have to study that bit of history in more detail. It is fundamental to the contemporary state of SR. Link to comment Share on other sites More sharing options...
Mordred Posted January 23, 2015 Share Posted January 23, 2015 It is fundamental to the contemporary state of SR. Makes it even more motivating for me to study his work. Any particular article recommendations? ( no limit on technicality) I've always been a firm believer in learning how our models developed historically. This includes major counter theories. Link to comment Share on other sites More sharing options...
xyzt Posted January 23, 2015 Share Posted January 23, 2015 Makes it even more motivating for me to study his work. Any particular article recommendations? ( no limit on technicality) I've always been a firm believer in learning how our models developed historically. This includes major counter theories. I can do better than that, the whole story of the development of the test theories of SR is explained extremely well in this book: Y.Z. Zhang, Special Relativity and its Experimental Foundations, World Scientific (1997) Link to comment Share on other sites More sharing options...
Mordred Posted January 23, 2015 Share Posted January 23, 2015 Many thanks mate hard copies on order http://www.amazon.com/Relativity-Experimental-Foundations-Advanced-Theoretical/dp/9810227493 Lol add that to my 20+ collection of physics related books. Ps my wife always asks "Why are you so interested in this universe stuff, you will never go there" My response " I'm already there" After 15 years she still doesn't get it lol Looking over some of the reviews his take on the one way vs two way influences on photons may or may not provide insight beyond what I already understand. Knowledge is always good regardless of perspective. Link to comment Share on other sites More sharing options...
xyzt Posted January 23, 2015 Share Posted January 23, 2015 Many thanks mate hard copies on order http://www.amazon.com/Relativity-Experimental-Foundations-Advanced-Theoretical/dp/9810227493 Lol add that to my 20+ collection of physics related books. Ps my wife always asks "Why are you so interested in this universe stuff, you will never go there" My response " I'm already there" After 15 years she still doesn't get it lol Looking over some of the reviews his take on the one way vs two way influences on photons may or may not provide insight beyond what I already understand. Knowledge is always good regardless of perspective. You are welcome, it is a good book. Link to comment Share on other sites More sharing options...
JohnSSM Posted January 24, 2015 Author Share Posted January 24, 2015 "the moon and sixpence" an amazing novel by Somerset Maugham about pressure and reactions... Link to comment Share on other sites More sharing options...
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